1. Field of the Invention
The invention relates to methods and apparatus for impregnating continuous lengths of fiber and filament structures such as yarns, with polymeric resins.
2. Brief Description of the Prior Art
A wide variety of methods and devices have been proposed for impregnating yarns and like structures composed of textile fibers and/or filaments with polymeric resins; see for example the U.S. Pat. No. 3,413,186 which describes the impregnation of yarns of glass fibers. In general, one of the problems faced by the artisan has been the achievement of a product wherein the multitude of individual filaments or fibers such as glass fibers is completely wetted and encapsulated with the resin impregnant so as to eliminate air pockets or voids between fibers. Unless this is accomplished, the resin will be insufficiently reinforced, thereby leading to lower than expected strength as indicated by modulus measurements. This of course .leads to a reduced life for the structure made up of the filaments or fibers. The problem is especially difficult when the polymeric resin is a relatively viscous thermoplastic resin of a desirably high inherent viscosity.
Another problem of the prior art relates to effecting a spreading of the fibers or filaments from each other so that the impregnant can thoroughly "wet" and encapsulate the individual fibers or filaments. The prior art is replete with descriptions of methods and apparatus having an objective of solving this particular aspect of the above-described problems. Representative of such descriptions are those found in the U.S. Pat. No. 2,730,455 to Swann, concerning filament separation by an electrostatic force; U.S. Pat. No. 3,413,186 to Marcoccli where elements are provided to flex and bend the multi-filament or fiber length during its residence in an impregnating fluid; U.S. Pat. No. 3,422,796 to Baber which describes the mechanical separation of multifilaments on a grooved surface; U.S. Pat. No. 3,779,844 to Dorsch who employed vibrators to effect the desired separation; U.S. Pat. No. 3,798,095 to Hall who employed acoustic vibrations; U.S. Pat. No. 4,312,917 to Hawley who in an effort to simplify apparatus merely inserted lobes in the path of the multifilament length during its contact with the impregnant; and U.S. Pat. No. 4,541,884 to Cogswell et al. which describes the use of series of rods which function as "spreader surfaces". The latter patent is particularly noteworthy because it describes a method and apparatus having a purpose to solve one of the problems solved by the present invention, i.e.; the uniform and thorough impregnation of a continuous length of a multifilament yarn with a relatively high molecular weight, relatively viscous polymeric resin. However, the improvements noted by Cogswell et al. are not entirely related to the apparatus, but are also dependent on the use of a volatile plasticizer in admixture with the thermoplastic resin. Such a condition is not always acceptable to the artisan who may be severely restricted by the environmental impact of disposal of the volatilized plasticizer. Also, the presence of a plasticizer in certain proportions may be degradative of the resin.
Also of interest for its representation of the state of the art, is the description given in the U.S. Pat. No. 3,694,131.
The apparatus and the method of the present invention provides a simplified means of completely wetting and impregnating a continuous length of multifilament or multifibered yarns with a thermoplastic polymeric resin of both relatively high and relatively low viscosity.